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Silverlight isn't going away. Microsoft insists it won't. Unfortunately, even after two rounds of comments by Bob Muglia, president of Microsoft's server and tools business, developers are still having a hard time envisioning exactly what Silverlight's future will look like.

The consternation first arose during Microsoft's Professional Developers' Conference (PDC) last week. Microsoft watcher Mary-Jo Foley, observing that the show was remarkably slim on Silverlight content, approached Muglia about it. Muglia explained that "Silverlight is [Microsoft's] platform for Windows Phone 7 development," but that where cross-platform Web content was concerned, the company's "strategy has shifted" toward HTML5.

Those remarks naturally caused some alarm, particularly among those who were accustomed to viewing Silverlight as Microsoft's answer to the Adobe Flash and AIR platforms. For some, it was the first indication that Microsoft has opted to cede the rich Internet application (RIA) market to Adobe and pursue a pure-HTML strategy.

Is Silverlight's top rival Flash or HTML?Muglia tried to clarify his comments in a post to the Silverlight Team Blog earlier this week. "The purpose of Silverlight has never been to replace HTML," he wrote, "but rather to do the things that HTML (and other technologies) can't, and to do so in a way that's easy for developers to use."

For many developers, however, the question has never been whether Silverlight will replace HTML, but whether (or indeed when) HTML and its related standards will evolve to the point that they can replace Silverlight and other plug-in-based RIA technologies. With Microsoft joining Google and others in aggressively promoting HTML5 as the future of cross-platform Web applications, that moment seems close at hand.

Evidence of a strategic shift at Microsoft was visible even before Muglia's PDC comments. Microsoft's Office 2010 Web Apps, for example, are built primarily with standards-based HTML, CSS, and JavaScript; Silverlight is completely optional and its use is limited to a few minor cosmetic enhancements. Microsoft's seeming reluctance to eat its own dog food hardly inspires confidence, especially with the company now touting the forthcoming Internet Explorer 9 as a leader in HTML5 support.

So how should prospective Silverlight developers interpret these latest turns of events? Should they press onward with the platform despite Microsoft's seeming ambivalence, or should they abandon it for a safer alternative? There are arguments to be made on both sides.

The case for developing with SilverlightIn the "pro" column, Silverlight still has a lot going for it. Classically trained developers often prefer it to Flash because it mimics the Windows development model and allows them to use their customary tools, such as Visual Studio. It's a geek's RIA solution.

It's also still reasonably cross-platform, despite Microsoft's backpedaling. After all, the vast majority of desktop clients are either Macs or Windows PCs, and Silverlight supports the most popular browsers on both. There's even an open source Linux port available via the Mono project, and while it's not as fully featured as its commercial cousins, it suffices for many apps.